The first notion I agree with.

The second is irrelevant to the notion you are defending : that sidechains seperate the BTC unit from its blockchain. SPVproof is a different trust model for this mechanism and the fact that is it embedded in the protocol makes it potentially more secure and trustable. Yes federated models sit on top of the protocol by the separation is the same, only the way by which these units interoperate with the mainchain is different.